A technique of graft polymerizing unsaturated carboxylic acid or its derivatives (e.g., its anhydride) to an ethylenic homopolymer or ethylenic copolymers containing ethylene as a major component has already been known.
In particular, a modified polyethylenic resin in which acrylic acid or maleic acid or maleic anhydride is graft polymerized, has been put into practical use as an adhesive material for various laminates containing, as constitutional materials, polar resins such as a polyamide resin, a saponified product of an ethylene-vinyl acetate copolymer, a thermoplastic polyester resin, a polyvinyl chloride resin, a polyvinylidene chloride resin and the like, and metallic foils such as an aluminum foil and the like, and for coating of a metallic plate or a metallic pipe.
Moreover, it is widely used for purposes of imparting functions such as affinity, compatibility and so forth to a matrix resin in composite materials in which various additives such as a filler, a reinforcing agent, a pigment and the like are compounded, and to a matrix resin in polymer-blended materials in which different resins are blended.
Although a number of modified polyethylenic resin of this type have been proposed, it is difficult to satisfy all the various characteristics required in the market, using a single modified polyethylenic resin. Thus, in order to impart the characteristics, a number of proposals have been made; for example, the type of polyethylene in the modified polyethylenic resin is changed, and to the modified polyethylenic resin, various other specified polyolefinic resins, various elastomers, various polymers having a polar group or compounds having a polar group and the like are compounded.
For example, compositions in which an elastomer resin is compounded to a modified polyolefinic resin (e.g., Japanese Patent Publication No. 18251/1980, Japanese Patent Application Laid-Open Nos. 132345/1986 and 18258/1987, and Japanese Patent Publication No. 36217/1985), and compositions in which to a modified polyethylenic resin, other polymers (e.g., a saponified product of an ethylene-vinyl acetate copolymer, or a thermoplastic polyethylenic resin) are compounded (e.g., Japanese Patent Application Laid-Open Nos. 39381/1978, 124080/1977, 103480/1977) are proposed.
In addition, it has been proposed in recent years to impart the above characteristics or increase heat resistance and adhesive properties by using, as a base material of a modified polyethylenic resin and a compounding agent for the modified polyethylenic resin, a linear low density polyethylene resin having properties that environmental stress cracking resistance (ESCR), heat sealability, low temperature characteristics and the like are excellent (the linear low density polyethylene resin is hereinafter sometimes referred to as "L-LDPE" (Japanese Patent Application Laid-Open Nos. 170940/1982, 68351/1982, 276808/1986, 18258/1987, 25139/1987, 119247/1987).
Of these proposals, Japanese Patent Application Laid-Open No. 170940/1982 discloses a polyolefinic resin composition which comprises (a) 30 to 100 wt% of a moderate or low pressure processed copolymer of ethylene and 0.2 to 20 mol% of .alpha.-olefin, having a density of 0.900 to 0.940 g/cm.sup.3, and (b) 70 to 0 wt% of other polyolefin resin, at least one of the components being graft polymerized. This is intended to provide a polyolefinic resin composition excellent/in adhesive properties and environmental stress cracking resistance (ESCR). However, as shown in Examples 1 to 6 and Table 1 thereof, the density of the moderate or low pressure processed polyethylene resin is 0.920 g/cm.sup.3, and there is no concrete disclosure, as described hereinbelow, about the density range (0.890 to 0.910 g/cm.sup.3) of the linear very low density polyethylene resin (which is hereinafter sometimes referred to as "L-VLDPE"). Moreover, the total amount of the graft modified L-LDPE and the unmodified L-LDPE in the composition described therein is 80 to 100 wt%, and the proportion of the resins in the total composition is markedly large. Furthermore, the composition fails to provide those products sufficiently satisfactory in fuel oil resistance, heat resistance and stiffness aimed at by the present invention.
In addition, in Japanese Patent Application Laid-Open No. 68351/1984 (Japanese Patent Publication No. 5614/1989), the same objects as above are intended to attain, and there is disclosed a laminate of a layer of a saponified product of an ethylene-vinyl acetate copolymer, a polyamide resin or a thermoplastic polyester resin, and a layer of a polyolefinic resin, wherein the laminate uses a polyethylenic resin composition comprising 99.9 to 65 wt% of an unmodified L-LDPE and 0.1 to 35 wt% of a graft modified L-LDPE or a high density polyethylene resin (which is hereinafter sometimes referred to as "HDPE"). As the unmodified L-LDPE and the graft modified L-LDPE, a linear polyethylene resin having a density of 0.910 to 0.960 g/cm.sup.3 (preferably 0.915 to 0.930 g/cm.sup.3 ; 0.926 g/cm.sup.3 in the example) is used.
Japanese Patent Application Laid-Open Nos. 276808/1986 and 167308/1987 provide a process of production for obtaining a modified product of high graft efficiency by decreasing contamination of the graft modified product obtained and cross-linking or oxidation reaction occurring at the time of graft modification, by using particularly L-LDPE having a density of 0.900 to 0.940 g/cm.sup.3 Japanese Patent Application Laid-Open No. 18258/1987 provides a graft modified polyolefinic resin using L-VLDPE having a density of less than 0.910 g/cm.sup.3 as produced by a gas-phase low pressure method, a mixture of the above polyolefinic rein and different material, and the like. As this different material, an unmodified elastomer (e.g., an ethylene-propylene copolymer rubber), polyolefinic resins such as a high pressure processed low density polyethylenic resin, an ethylene-ethyl acrylate copolymer, an ethylene-vinyl acetate copolymer and the like, a polyamide resin, a saponified product of an ethylene-vinyl acetate copolymer, and the like are given.
In addition, Japanese Patent Application Laid-Open No. 25139/1987 provides a material excellent in moldability and adhesive properties, which is a composition comprising a high pressure processed low density polyethylenic resin as specified by a product of a melt flow rate (hereinafter sometimes referred to as "MFR") and a melt tension, and MFR, and a modified polyethylenic resin resulting from graft modification with acrylic acid or maleic anhydride of a copolymer (linear very low density polyethylenic resin) of ethylene and a-olefin, having a density of 0.880 to 0.900 g/cm.sup.3.
In addition, in Japanese Patent application Laid-Open No 10107/1987, there are proposed a modified polyethylenic resin of a copolymer comprising ethylene and .alpha.-olefin having at least 4 carbon atoms having a density of 0.890 to 0.910 g/cm.sup.3, a weight average molecular weight/number average molecular weight ratio of 2 to 15, and a product of melt tension and MFR at a temperature of 160.degree. C. of not more than 4, and a composition of the above modified polyethylenic resin and an unmodified polyethylenic resin.
Furthermore in Japanese Patent Application laid-open Nos. 131345/1986 and 132377/1986, there are proposed an adhesive resin and its laminate, the adhesive resin being obtained by adding 1 to 40 parts by weight of rubber to 100 parts by weight of a copolymer of ethylene and .alpha.-olefin, having a density of 0.860 to 0.910 g/cm.sup.3 a boiling n-hexane insoluble content of at least 10 wt%, and a maximum peak temperature as determined by a differential scanning colorimeter (DSC) of at least 100.degree. C., or a composition of the above copolymer as a major component and a polyolefinic resin, and then by graft modifying the copolymer or the composition.
In addition, in Japanese Patent Publication No. 36942/1985, there is proposed a multi-layer laminate comprising a polyolefinic resin composition and a polyamide resin layer, the composition comprising 99 to 50 wt% of a polyethylenic resin having a degree of crystallization of at least 40% or a graft modified product of polypropylene having a boiling n-hexane insoluble content of at least 80%, and 1 to 50 wt% of an ethylene-.alpha.-olefin copolymer having a degree of crystallization of 5 to 30% and a density of 0.870 to 0.910 g/cm.sup.3, which is a laminate markedly improved in interlaminar adhesive properties, particularly interlaminar adhesive properties at the time of being dipped in boiling water. As the most preferred ethylene-.alpha.-olefin copolymer, an ethylene-butene-1 random copolymer having a density of 0.870 to 0.900 g/cm.sup.3, an ethylene copolymerization ratio of 85 to 95 mol% and a degree of crystallization of 5 to 30%, as polymerized by the use of a vanadium-based catalyst, is given.
However, even if any of the modified polyethylenic resins or compositions thereof is used, it is quite difficult to provide a material excellent in fuel oil resistance. (gasoline resistance) and impact resistance as aimed at by the present invention and further having good affinity and adhesive properties. For example, as the material for use in industrial Chemical can and containers of fuel, such as gasoline, which are used for a long time at low to high temperatures, and further as related car parts, it is required to sufficiently satisfy all the above various physical properties. Particularly, these physical properties are strongly required for an adhesive layer between a polyamide resin layer and a polyethylenic resin layer to be used in a multi-layer polyethylenic resin fuel container (e.g., five layers comprising three different materials) containing the polyamide resin layer, for example, provided for the purpose of preventing permeation of the fuel oil such as gasoline. Similarly, the aforementioned inventions that have been proposed so far fail to obtain sufficiently satisfactory material.
That is, even if an elastomer such as synthetic rubber is added to a graft modified polyethylenic resin or its composition in order to increase impact resistance, or an ethylene-.alpha.-olefin copolymer polymerized in the presence of a vanadium-based catalyst as a main catalyst or a graft modified polyethylenic resin made mainly of L-VLDPE and having a density of 0.890 to 0.910 g/cm.sup.3 or its composition is used, the fuel oil resistance is seriously poor in use at high temperatures and for a long time. Moreover, with the graft modified HDPE alone or the composition of the graft modified HDPE and the unmodified HDPE or unmodified low density polyethylenic resin, for example, it is difficult to obtain greatly excellent impact resistance even if the fuel oil resistance is satisfied, and it is also difficult to obtain good affinity and adhesive properties to the aforementioned various resin materials and metallic materials.
To take as an example a molding of profile shape as produced by blow molding, several to several ten percent of burr is usually produced, and this burr is generally recycled for reuse from an economical standpoint. In the case of a multi-layer structure, in particular, produced for the purpose of preventing the permeation of contents to the outside of the container by using a barrier material of a polyamide resin (PA), a saponified product of an ethylene-vinyl acetate copolymer and the like, the barrier material is usually contained in the burr and recycled for reuse.
It is known that the impact resistance of the barrier material is markedly inferior to that of HDPE having a relatively high molecular weight as generally used in blow molding, and the barrier material has a disadvantage of being poor particularly in impact resistance at low temperatures. Therefore, in order to produce containers of multi-layer structure on a commercial scale and economically, the burr containing the material poor in impact resistance is recycled and used in the layer of the main material, the impact resistance of the container is decreased and it becomes difficult to satisfy the required performance.
Needless to say, in order to solve the above problem, there has been proposed a method in which a layer for recycling the burr is additionally provided in the multi-layer structure, or the burr is incorporated into the adhesive layer for bonding the main material (mainly a polyethylenic resin) and the barrier material for the purpose of recycling thereof. However, the former method is not economical in that it needs an additional apparatus for producing the multi-layer structure, and the latter method is not desirable in that the barrier material (e.g., PA) in the burr reacts with the graft group of the graft modified polyolefinic resin, thereby causing gelation, and long term adhesive durability is poor.
For the above reasons, as disclosed in, for example, Japanese Patent Publication No. 34461/1985 (Japanese Patent Application Laid-Open No. 113678/1979) and Japanese Patent Publication No. 42625/1986 (Japanese Patent Application Laid-Open No. 91634/1980), it has been proposed to use a specified polyolefinic resin or polyamide resin excellent in adhesive properties for the purpose of preventing a decrease in the impact resistance of the resulting product. In these inventions, however, the respective resins are poor in fuel oil resistance over a long period of time and unsuitable for practical use.